There is an urgent public health need to develop more effective and well tolerated treatments for patients with major depressive disorder (MDD); cognitive training interventions aiming to modify cognitive and affective processing abnormalities underlying MDD represent a promising new strategy. This research project translates a well established cognitive bias in major MDD, working memory bias, into a novel intervention target. In a double-blind, randomized, controlled study, MDD participants undergo 6 weeks of cognitive training sessions, with three sessions per week.